1. Field of the Invention
The invention relates to an instrument kit for performing spinal stabilization by means of a bone-anchoring element of the screw type and using posterior or postero-lateral routes.
The instrument kit according to the invention is intended particularly, but not exclusively, for posterior surgical osteosynthesis of the lumbar, thoracic or even cervical spine, using minimally invasive routes or open surgery.
In cases of anatomical dysfunction of the vertebral column, bone anchors in the form of pedicle screws or vertebral screws are placed in the vertebrae, which are connected to each other by rod-type or plate-type connecting elements.
More particularly, the invention relates to the field of disposable instrument kits packed in a sterile state and comprising all the tools necessary for performing a surgical intervention for inserting pedicle screws without recourse to additional instruments.
2. Prior Art
The international application WO 2005/016183 is also known. The application describes a kit of implants of the vertebral plate and screw type combined with disposable instruments packed in a sterile state. Besides the disadvantage of providing only a single diameter and length of screw for the bone anchoring, this application describes only a single type of instrument, a screwdriver bar and its handle. This international application does not propose a technical solution for the design and production of instruments subjected to high mechanical stresses. Consequently, this sterile kit on its own does not allow a surgical intervention to be performed without also using traditional instruments, requiring re-sterilization after each intervention. The reason is that it is difficult to reconcile the constraints of low production costs, a necessary condition for disposable instruments, and the qualities of mechanical strength, a necessary condition for instruments subjected to high stresses during their use by the surgeon.
In the prior art, a spinal device described in US patent application US2004/138662 has been proposed, comprising a slotted tube with, at its proximal end, a means for fastening a screw. The distal end is articulated by a hinge, making it possible to move the proximal ends of the two branches apart in order to free the head of the screw and permit the withdrawal of the tube after implantation of the screw.
Within the meaning of the present application, “proximal” signifies nearest to the site of spinal intervention, and therefore the end farthest from the operating surgeon, and “distal” signifies the end remote from the spinal zone and therefore accessible by the operating surgeon. The screw is fixed on the proximal end.
International patent application WO2007/092870 describes another solution for a spinal device formed by a tube with pincers at its proximal end.
US patent application US2005/0192570 proposes another embodiment of a spinal device composed of a tube with a longitudinal slit and a slotted proximal end permitting the fastening of a screw and release by spreading apart of the proximal end.
The solutions in the prior art proposing that the screw be released by spreading apart the proximal ends of the screw-supporting tube are not satisfactory since they require a sufficient space in the zone surrounding the screw in order to permit disconnection. However, in this zone, the presence of the bone part often limits the available space and may lead to difficulties in releasing the tube from the head of the screw.
Moreover, the forces that need to be transmitted for radially disengaging the proximal end of the tube from the head of the screw are substantial and involve maneuvers that are not especially ergonomic at a distance. The release of the screw involves actions that can also lead to the operating site being concealed during this delicate phase of the intervention.
US patent applications US2008/0262318 and US2009/022045 describe a tissue retractor made of a flexible plastic material, and a means for withdrawing the retractor by rupture of a weakened zone provided in the proximal part of the retractor. The retractor has two flexible branches joined at their proximal end by a zone of permanent connection to the head of the screw. The distal ends of the two branches are free to allow a transverse force to be exerted, with the object of ensuring a pressure tending to spread apart the margins of the muscle tissues. The object is to allow the surgeon to view the zone of implantation of the rod on the pedicle screws without introducing an additional retractor.
Between the distal end of the two flexible branches and the zone of permanent connection to the head of the screw, a weakened zone is provided for disconnecting the screw from the two branches at the end of the intervention.
This retractor from the prior art poses a risk of unintentional rupturing of the weakened zone when a force is applied to the two flexible branches in order to spread the tissues apart. The compromise between the flexibility allowing the two branches to be spread apart at an angle and the required rupture for withdrawing the instrument is delicate. If the weakened zone is too strong, the surgeon may certainly apply considerable forces to the margins of the incision, but he will have to apply excessive and sometimes invasive forces when disconnecting the retractor from the screw. If it is not strong enough, the surgeon risks breaking the retractor inadvertently during the intervention.
Moreover, the transverse forces to apply for spreading the tissues apart impact axially on the screw, because of the connection of the screw and the branches of the retractor.
Moreover, this device does not allow the whole surgical intervention to be performed, and in particular it does not provide the instrumentation for placement of the rod, and then of the element for blocking the rod on the pedicle screw.